Basics of Geometry1.4 Intersections

1.5 Segments

ReviewThe intersection of two lines is a

___________.The intersection of two planes is

a ________.Any three points can define a

___________.Any two points can define a

________.

LINE

LINE

POINT

PLANE

Review Name 4 coplanar

points. Are A, D, and E

coplanar? Are A, D, G, and F

coplanar? Are E and F collinear? Give plane ADC

another name.

A

B C

D

E F

GH

Intersections of Lines Name the intersection

of and Name the intersection

of and Name the intersection

of and

AC BE

AC

BE DF

DF

A B C

D E F

Intersections of Planes Name the intersection

of planes S and R. Name the intersection

of planes R and T. Name the intersection

of planes T and S.

S

R

T

k

l

Sketch It!

Sketch and label a plane. Draw and label a line that is in the plane. Draw and label a line that does not

intersect the plane. Draw and label a line that intersects the

plane at one point.

Pj

lk

Sketch It!

Sketch and label two planes that intersect.

S

Rk

Assignment :

First, we will discuss page 17.

Then, quietly work on your own work. I will help if you need it.

p. 11: 8, 14, 24, 36, 38

p. 17: 16 – 32 even

Segments

A segment is a part of a line. A segment has a length. To find the length of a segment (or the

distance from beginning to end), subtract the coordinates of the endpoints and take the absolute value.

12 xx

Segments Continued

The notation for distance is simply the endpoints of the segment.

Thus, the formula for distance on a line segment is:

AB

12 xxAB

Find AB

-5 13A B

12 xxAB )5(13 AB 18

Segment Addition Postulate

If B is between A and C, then AC = AB + BC

If AC = AB + BC, then B is between A and C

A B C

Find EF

D E F

16

10

EFDEDF EF1016

10101016 EFEF6

Find AB

C A B

29

15ABCACB AB1529

15151529 ABAB14

Find DF

D E F12

EFDEDF 712 DF

19DF

7

Congruency

Shapes that have the same dimensions are called congruent.

Two segments who have the same length are called congruent.

The symbol for congruency is

Congruent Segments

Congruent segments are often marked with a short tick mark.

A B

C D

CDAB

Congruent Segments

Sometimes multiple tick marks will be used.

R S

TH

HTRS STRH

Assignment

Pages 31 – 33

1 – 28